Motion monitor

ABSTRACT

A method for evaluating the motion of a moveable object relative to a reference object includes locating the reference object within a three-dimensional coordinate system having first, second, and third positional coordinates such that the position of the reference object is characterized by respective values of first, second, and third positional coordinates. A mechanism is provided having a plurality of visual indicators. A sensor is configured to detect the position of the moveable object within the three-dimensional coordinate system substantially apart from any dynamic property inherent in the movement of the moveable object. An acceptable minimal number of sampling events is determined and providing a sensor having sufficient response rate as to be capable of determining respective positions of the moveable object as the moveable object moves relative to the reference object such that the number of the respective positions exceeds the acceptable minimal number for any maximum velocity of the moveable object manually achievable by the user.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims be the benefit of U.S. Provisional App. No.60/857,125, filed Nov. 7, 2006, and U.S. Provisional App. No.60/874,320, filed Dec. 13, 2006.

BACKGROUND OF THE INVENTION

The present invention obtains movement information about the movement ofa mechanical device.

In many cases it is desirable to obtain movement information about themotion of a golf club head in order to be able to properly modify itsswing.

The foregoing and other objectives, features, and advantages of theinvention will be more readily understood upon consideration of thefollowing detailed description of the invention, taken in conjunctionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 illustrates a six dimensional coordinate system.

FIG. 2 illustrates movement through a sensor detection range.

FIG. 3 illustrates a typical sensor output.

FIG. 4 illustrates constant distance movement within a sensor detectionrange.

FIG. 5 illustrates two overlapping sensor ranges.

FIG. 6 illustrates three overlapping sensor ranges.

FIG. 7 illustrates a golf swing monitor.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

A data acquisition system (DAQ) may be used to capture the vectormovement (magnitude and direction) of an object traversing a complexpath in three dimensions and extract the constituent movements into asix dimensional coordinate space (or other number of dimensions). A golfclub swing is used as an illustrative example of a complex mechanicalmovement. A three dimensional (3D) Cartesian coordinate axes (X, Y, Z)is shown in FIG. 1. The golf club head swings primarily along thedirection of the Z axis. The Y axis is in the vertical directionrepresenting the height of the club above the ground, and the X axisrepresents the side-to-side (S2S) position of the club. The origin ofthe axes is centered on the golf ball, i.e. the center of the ball islocated at the intersection of the X, Y, and Z axes. Each axis has alinear and rotational movement associated with it. Linear movements aremeasured along each axis while rotational movements are measured abouteach axis. The three axes times the two movements (linear, rotational)produces the six dimensional measurement space described above.

Complex mechanical movement can be decomposed into a set of orthogonal(independent) component (constituent) movements. The original movementcan be reconstructed from these component movements by adding them backtogether into a “superposition.” The data acquisition system (DAQ) maycapture and decompose a complex mechanical movement into orthogonallinear and rotational components. The coordinate axes system used hereis a three dimensional Cartesian coordinate system (three orthogonalaxes X, Y, Z). Any valid coordinate system may be used with thisapplication, i.e., cylindrical, spherical, etc.

Movement along any one axis of a Cartesian coordinate system isindependent of the other two axes. In other words, a movement directlyalong the X axis for example, is not visible on the Y or Z axes. This isadvantageous to a user who needs to investigate individual components ofa complex movement. For example, this could be applied to the area ofanalyzing a golf club swing. A golf club, during normal use, travelsthrough a three dimensional space in a highly complex manner, i.e. ithas many linear and rotational components along multiple axes.Decomposing such a complex movement into basic constituents (i.e., headrotation about the vertical axis, head velocity along the direction ofthe swing, etc.) greatly simplifies the task of improving the completegolf club swing because the user can isolate a component of the swinggiving him/her trouble and work on it.

Every movement (linear, rotational) is described by three relatedquantities, position, velocity, acceleration (PVA). Each of these can berepresented mathematically in the time domain as x(t) (position), v(t)(velocity), and a(t) (acceleration.) They are related through thedefinitions,

${{v(t)} = \frac{x}{t}},$

${a(t)} = {\frac{v}{t}.}$

Each of these quantities (PVA) can be positive, zero, or negative.Because they are mathematically related to each other, measuring one canproduce the other two.

A complicated vector movement of an object traveling through a threedimensional space can be described by providing values for each of the6D coordinate space components of the object's movement. The totalnumber of components required to produce a complete description is threelinear axes (X, Y, Z) plus three rotational axes (X, Y, Z) times threequantities (PVA) or eighteen.

The data acquisition system (DAQ) are designed specifically to allowaccurate movement decomposition. The sensors should have the capabilityof producing data rich enough in content from which the software canextract the 6D components. These two pieces of the DAQ (hardware,software) should be designed together in order to function well.

For purposes of explanation here the complex mechanical movement beingcaptured, recorded, and deconstructed, will be produced by a golf clubduring normal play or practice. The system tracks the movement of amechanical object through space with respect to time. The movement isrecorded then dissected into six dimension (6D) parameters (describedabove) in order to provide a deep understanding of the complex movementfor the user.

Sensors are used to track the complex movement of an object. In orderfor this system to function properly there are minimum requirements onthe sensors. They need to be able to respond fast enough to capture muchof the high frequency component of the movement. They also should beable to capture the low frequency component, typically a stationaryposition. The output of a sensor should depend only on the distance ofthe object from the sensor and not on the speed of the object movingpast the sensor. This characteristic allows the system to measure speedand distance independently.

Referring to FIG. 2, an object traveling through the range of a sensor,shown as a hemisphere, will produce a signal dependent on the distanceto the sensor. When the object first enters the sensor range a weaksignal is produced. As the object continues to travel towards the sensorthe signal strength continues to increase. At the point where the objectis closest to the sensor the signal reaches its maximum value. As theobject travels away from the sensor the signal strength decreases. Thesignal returns to zero when the object leaves the range of the sensor.

In order to create an accurate temporal snapshot of the movement of anobject through the sensor detection range some technique of datacollection with memory should be employed. A micro-controller (μC) canbe used to create such a picture in time. A μC having all the necessarycomponents to collect and store sensor data may be used. A technique ofadapting the sensor output signal to a μC input is utilized. Forinstance, many sensors have analog outputs. A μC having an analog todigital converter (ADC) is easily found. Simple electronic interfacecircuitry insures that the sensor output signal is compatible with theμC input circuit. The μC can be programmed to collect and store sensorsignals at known time intervals. All the sensor signals are stored suchthat the time of occurrence of each signal is known. The sensor signalscan be read-out in correct order to create an accurate temporal pictureof the sensor signal.

Referring to FIG. 3, as an example, the graph illustrates an actualsensor output of a mechanical object traveling on a straight line paththrough the sensor detection range. More than 200 samples of the sensoroutput were collected and stored during the object's travel. The samplesare treated as a single quantity because they all reside in a singlefile. This file is available to be processed by the μC at some latertime.

Typically the sensors are sampled many times in rapid succession. Thesesamples are then assembled to create a virtually continuous picture intime of the sensor signal. This provides the necessary accuracy andrichness of information that allows more than one quantity to beextracted from each sensor, i.e., peak amplitude, average amplitude,pulse width, etc., during post-processing.

A single sensor can typically discern only the distance to an object,not the path taken. For instance, if an object travels at a constantdistance from the sensor within its sensing range the sensor willproduce a constant signal. Referring to FIG. 4, as an example, a sensoris illustrated with a circular path (broken line) above it at a constantdistance from it. If an object is anywhere on this line eitherstationary or traveling at a constant or varying speed, the outputsignal from the sensor will always be the same value. The sensor canonly detect distance. Since the distance is constant the signal is alsoconstant. This is an ambiguous situation. The position, velocity, andacceleration (PVA) of the object are unknown.

A top-down view of the sensor detection range is a circle with thesensor at the center. The only information that can be determined whenan object is sensed inside this circle is the distance from the sensor.Adding a second sensor provides additional information which can be usedto reduce the PVA ambiguity. The two sensors are placed so that theirdetection ranges overlap each other. If the two sensors are placed inthe same plane, a top-down view of their sensing range would be two overlapped circles, as is shown in FIG. 5.

The single cross-hatched area between the two sensors (Sn1, Sn2) iswhere the two detection ranges overlap. If the object being tracked isin this area additional information about its PVA can be obtained bycomparing the output signals from Sn1 and Sn2. The PVA of the objectalong the direction of the line B-B within the single cross-hatched areacan be determined. A third sensor is added in order to remove the PVAambiguity along the direction of the line A-A. The optimum location forthis third sensor would be directly on the line A-A though it could alsoreside else where (as long as it's not on the line B-B).

Referring to FIG. 6, an illustration of using three sensors is shown.The layout begins with the two sensor configuration shown above thenadds a third sensor (Sn3) on the line A-A. This allows a triangulationof the signals in order to determine the object PVA within the doublecross-hatched area. Using three sensors may be adequate for oneapplication but not for another. Each application is analyzed in orderto determine the optimum sensor quantity, placement, and softwaredeconstruction semantics. This places responsibility on the designer tocreate a sensor layout and software design together that will work for aparticular application. A special application would be a golf swingmonitor.

When used to monitor the movement of a golf club head during a swing onepreferred embodiment places the sensors in the immediate vicinity of thegolf ball. This could be due to a limited sensor detection range. Thismotion (swing) monitor would also contain a display for the user. FIG. 7shows one embodiment of a swing monitor. In the illustration the displayarea is denoted by the recessed area around the golf ball. The sensorsreside under the golf ball. The swing monitor is placed on the groundwith the display facing the user. The user places a golf ball on it in apre-determined location then hits the ball in a normal fashion. A golfball tee may or may not be used with the swing monitor. The display onthe surface shows properties of the swing that resulted in the vicinityof the ball.

The motion monitor would be battery operated and completely selfsufficient, i.e. it would not need to be interfaced to a laptop ordesktop computer in order to operate. The μC on board the system iscapable of providing all the functions necessary for the system tooperate. The small size and self-sufficiency allows this motion monitorto be highly portable and very useful in almost any location.

One type of sensor that could be used with a swing monitor is a Halleffect magnetic sensor. This type of sensor has the sensor propertiesstated above, i.e.:

a. High frequency response.

b. Zero frequency response.

c. Output signal depends only on the distance to the magnet, notvelocity.

This sensor should include a magnet to be attached to or installedinside of the golf club head.

Some types of magnetic sensors will only operate when the magnet ismoving, (i.e., they will not sense a stationary magnet) these can becalled dynamic sensors. These sensors typically contain a loop of wireor an induction coil. These sensors are typically sensitive to twoparameters simultaneously, proximity and velocity. A single reading byone of these sensors will be the result of both the velocity of themagnet and the distance of the magnet to the sensor. This type of sensorwould not be optimum for a golf swing monitor.

The sensors chosen for the swing monitor of this example will operatewith non-moving magnets, i.e. they will sense a stationary magnet aswell as a moving magnet. These can be referred to as base-band sensors.These sensors are not sensitive to the magnet velocity as it passes thesensor, only proximity. These two properties are useful because theyallow a minimum number of sensors to detect a maximum number of movementproperties. For instance, when the user is “addressing the ball” theclub is not swinging, it is being placed in a stationary position behindthe golf ball prior to the swing. Base-band sensors will be able toacquire the static position/orientation of the golf club in thisinstance whereas dynamic sensors will not. When a swing is made thebase-band sensors will also be able to record the moving club.

Magnetic sensors are not the only type that will work with this motionmonitor. Any sensor that possesses the above described characteristicsand has an acceptable range of detection can be made to work. But notevery sensor is easy to work with, or has to optimum price range, orpower requirements, or size.

The sensors in this example motion monitor lie underneath the golf ballin a flat plane. The position of each sensor is defined by the size andstrength of the magnet on the moving object (in this case a golf club.)There is an optimum position for each sensor depending on whichparameter is being sensed. In order to simultaneously collect as many ofthe 6D parameters as possible, compromises have to be made on thepositions of all the sensors together. Deconstructing software is thenappropriately designed.

The micro-controller (μC) portion of the DAQ will collect all the sensorinformation, store it, and process it. Processing involves extracting 6Dcomponents of the complex movement for display. The μC can also drive(control) the display.

Sensor signal acquisition occurs through continuous sampling over time.Each sensor signal is recorded and stored in an array long enough tocontain all the vital characteristics of the movement. A single arraycontains a continuous picture of the sensor signal in time. After themovement has been recorded it is processed to extract the basiccomponents making it up. These 6D components are displayed for the userto see. The movement components are often more valuable to the user thanthe complex motion itself.

The terms and expressions which have been employed in the foregoingspecification are used therein as terms of description and not oflimitation, and there is no intention, in the use of such terms andexpressions, of excluding equivalents of the features shown anddescribed or portions thereof, it being recognized that the scope of theinvention is defined and limited only by the claims which follow.

1. A method for evaluating the motion of a moveable object relative to areference object comprising: (a) locating said reference object within athree-dimensional coordinate system having first, second, and thirdpositional coordinates such that the position of said reference objectis characterized by respective values of said first, second, and thirdpositional coordinates; (b) providing a mechanism having a plurality ofvisual indicators; (c) providing a sensor configured to detect theposition of said moveable object within said three-dimensionalcoordinate system substantially apart from any dynamic property inherentin the movement of said moveable object; (d) determining an acceptableminimal number of sampling events and providing a sensor havingsufficient response rate as to be capable of determining respectivepositions of said moveable object as said moveable object moves relativeto said reference object such that the number of said respectivepositions exceeds said acceptable minimal number for any maximumvelocity of said moveable object manually achievable by said user. 2.The method of claim 1 wherein said moveable object is the head portionof a golf club.
 3. The method of claim 1 wherein said reference objectis a golf ball.
 4. The method of claim 1 wherein said offset and saidarray of said first one of said indicators are linear.
 5. The method ofclaim 1 wherein said dynamic property is an angle of approach based onthe angle between an axis of intended trajectory of said referenceobject and an axis of motion of said moveable object as said moveableobject closely approaches said reference object as evaluated with eachsaid axis being projected onto a common plane within said threedimensional coordinate system.
 6. The method of claim 1 wherein saidsensor detects high frequency movements.
 7. The method of claim 1wherein said sensor detects low frequency movements.
 8. The method ofclaim 1 wherein said sensor detects zero frequency movements.
 9. Themethod of claim 1 wherein said sensor proves an output that isindependent of object speed.
 10. The method of claim 1 wherein saidsensors are positioned related to one another to detectmulti-dimensional movements.
 11. The method of claim 1 wherein saidmulti-dimensional movements are orthogonal.
 12. The method of claim 1wherein said movements are linear orthogonal.
 13. The method of claim 1wherein said movements are rotational orthogonal.
 14. The method ofclaim 1 wherein said movements include nine orthogonal linear componentsand nine orthogonal rotational components.